used Sony Mirrorless quest

I think that you should just stick with Canon rather than have to use adapted lenses

For convenience and a small package you can get a used nex6 with kit lens relatively cheap.

In truth any of the NEX/Alpha E-mount cameras will work with your canon lenses and the correct adapter.

What you need to consider is the feature set you want (Electronic Viewfinder or just LCD screen, 16 megapixels-20 megapixels-24 megapixels, CDAF autofocus or CDAF+PDAF autofocus, autofocus speed etc.) and the price range you want to play in. Unless you can specify these there isn't any intelligent advice we can give you.

If you really want the CHEAPEST (and I mean dirt cheap) pick up a first generation NEX-3. You can find used bodies for less than $80! http://amzn.to/2okhFT6 Pair it with a cheap manual adapter and you are good to go.

The thing is... although dated, the NEX-3 is a decent little camera. Sony did a firmware update that gives it focus peaking, a key feature when using adapted lenses.

Funny thing, I just went out and re-acquired a used NEX-3N for some just for fun photography with a great little, uncomplicated camera.

My choice would be the Nex-6, or even the Nex-5r/5t if you want cheaper and don't need the viewfinder. To buy the viewfinder for the Nex-5 cost more than the camera itself nowadays. Anyway, the camera bodies can be had dirt cheap, they are capable of outstanding images, and they shoot excellent 1080p video.

I kept my Nex-5r after buying the a6300. I use vintage Canon FD lenses on it (especially the 50mm 1.4), take it hiking, etc. It gets a fair amount of use.